Eco-Effective Decisions: Raise the Green Roof, Lower your Urban Heat Island

Editor's note: Please welcome Green Options' newest writer, Elizabeth Redmond. Elizabeth is a sustainable designer working in Ann Arbor, Michigan. Her past experiences include working with her sister Sara Snow on a Discovery Health TV series called Get Fresh with Sara Snow, where she researched sustainability and built environment content.
I asked Elizabeth to give me an "elevator pitch" of her focus here at Green Options. Her response:
Today's green products and services seem to be an eclectic collection of "lighter tread". I propose that we begin to design and interact with products and systems that encourage heavy treading, where a heavy active footprint is one step in the right direction without a half step in the other. My objective is to tell you how things work, and enable you with the information to make responsible, and conscious decisions about society, lifestyle, health, and sustainability.
More than tornadoes, hurricanes, snow, or cold weather itself, heat is the number one weather related cause of death in the United States. So urban dwellers (that means half of us in this world) beware! Much of our urban heat is due to a phenomena called the Urban Heat Island effect. An Urban Heat Island is a metropolitan zone that is warmer than the surrounding, less developed area. The EPA reports that "On hot summer days, urban air can be 2-10°F [2-6°C] hotter than the surrounding countryside”. What does this mean? It’s going to be a hot summer, but luckily we can do a couple of things to help cool your stroll down the sidewalk.
First, how does this phenomena work? It is all about the energy transfer of solar radiation to our built environment. Lets go back to high school physics and review. All you need to know is that heat from the sun (radiation) gets stored in our constructed impervious and dark surfaces such as concrete and pavement (insulators). During the day these surfaces of high heat capacity collectively act as a massive heat energy reservoir. (I.e.: concrete can retain nearly 2000 times the heat as an equivalent volume of air). Next, the heat on the surface of these materials mixes with the already hot air and you experience a hot gust that feels dense enough to chew on (convection).
About 5 hours after sunset is when we experience the greatest heat discrepancy. The stored heat seeps out of the concrete to be relieved by the cool air (conduction) and dissipates into the environment to raise our nightly air temperature. As you can tell, these thermally insulating materials that dominate city surface construction make it really darn hot for us.
What are the consequences?
- We pump up the air conditioner and demand more electricity from the grid.
- We sweat more and have to cool off, so we take more showers increasing our demand on the municipal water supply.
- We opt for quick and comfortable transit- our car or a cab instead of the subway
- We drink more ice- demanding more energy to cool that freezer down enough.
You can see where this is going. More heat equals more energy consumed for the comfort of our urban habitat. The Urban Heat Island Group estimates that the Los Angeles Heat Island costs the city $100 million in energy annually. According to the UN, close to half of the worlds population is living in urban areas today. So for that half of us living in cities, here are a couple of things we can do to control the city heat and why!
- Plant More Plants: living plants inhale CO2, use it in photosynthesis to make sugars aka "fuel", and exhale O2 into the air. They are nature’s fuel cell and luckily they like our exhaust (but this is no excuse to emit more). Plants also intercept solar radiation and cool the air through evaporitization.
- Raise the Green Roof: Green roofs benefit our environment as the aforementioned plants do; and, since they are so high up they intercept the heat before it can even reach our sidewalks. Encourage green roof development in your city, or just go do some guerrilla plant parenting on the roof of your building. Plus, what could better accompany your rooftop BBQ than some friends, beverages, and plants.
- Say no to Freon: Turn your thermostat 2°F. I do live in Michigan so I feel you, Houston: just try adjusting your thermostat by 1°F and help the city out. You will actively be reducing the risk of another black out or severe heat wave.
- Install a Rain Barrel (in your back yard or on the rooftop): It gives you free water from nature! You will conserve energy by not demanding it from the city municipal supply, and mitigate the erosion of harmful pesticides and fertilizers into the water table.
- Plant a Bioswale or Rain Garden: These are essentially green roofs on the ground. They filter rainwater and help to return clean water to the water table. In return our lakes, rivers, and oceans are cleaner, creating a cleaner evaporitization cycle, and thus cleaner air.
- Lay Pervious Pavement: This pavement allows the ground to breathe! It also filters rainwater as the aforementioned rain gardens. This might not be something you install on your own but it can certainly be encouraged at your office, or in your city.
- Take Public Transportation, or even better, Ride a Bike: Every bit of carbon dioxide we can keep out of the air this summer will make a big difference.
With these eco-effective tools to cool and clean the air this summer, you are on your way to an enjoyable commute to work, walk in the park, and rooftop BBQ.


June 12th, 2007 at 11:44 pm
Hi Elizabeth,
Welcome to the blogsphere! I read your article with interest. Here is a question though. I have lots of plants growing around my house (I am not really in the center of the city, but I am in part of the hottest area of LA), but to keep them growing through the summer means LOTS of watering. So would that be light treading? Solving one problem but creating another?
Keep up the good articles.
Love,
Judy Krueger
June 15th, 2007 at 4:26 pm
Elizabeth Redmond l Sustainabile Design